Solar cell, solar cell module using solar cell, and manufacturing method for solar cell

ABSTRACT

The present invention is to grant a margin in the control of a depth of a groove when removing a transparent insulation layer after the transparent insulation layer is formed on the entire surface of the transparent conductive layer, thereby provide a solar cell which has superior productivity in mass manufacturing. A solar cell includes an n-type amorphous silicon layer formed on a front-surface side of an n-type monocrystalline silicon the substrate; a front-surface side transparent conductive layer formed on the n-type amorphous silicon layer; a p-type amorphous silicon layer formed on a rear-surface-side of the substrate; and a rear-surface-side transparent conductive layer formed on the p-type amorphous silicon layer. A front-surface side collector electrode is formed by plating on the front-surface side transparent conductive layer whereas a rear-surface-side collector electrode is formed on the rear-surface-side transparent conductive layer by printing.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is based on International Application PCT/JP2011/056375which claims priority on the basis of Japanese Patent Application No.2010-064800.

TECHNICAL FIELD

The present invention relates to a solar cell of an improvedcharacteristic, a solar cell module using the solar cell, and amanufacturing method for the solar cell. In particular, the presentinvention relates to a structure of a front-surface-side collectorelectrode and a manufacturing method thereof.

Solar cells are expected as a new source of energy since they canconvert sun light which is a clean form and inexhaustible supply ofenergy, directly into electricity.

Solar cells are made from a semiconductor substrate which is made of acrystalline semiconductor material such as monocrystalline silicon andpolycrystalline silicon, or a compound semiconductor material such asGaAs and InP.

Among these solar cells, solar cells including a power generation layerprovided by a monocrystalline silicon substrate on which an amorphoussilicon layer is formed are now gathering attention because of theirability to reduce carrier recombination loss. Of particular interest isa solar cell which utilizes an arrangement where an intrinsic amorphoussilicon layer is placed between a monocrystalline silicon layer and anamorphous silicon layer of mutually opposing conductivity types forreduced defect in the interface and improved characteristics of heterojunction interface (hereinafter this solar cell will be called HIT(registered trademark) solar cell).

FIG. 15 is a sectional view showing a configuration of an HIT solarcell. Referring to FIG. 15, an intrinsic (i-type) amorphous siliconlayer and a p-type amorphous silicon layer 13 are formed in this orderon an n-type crystalline silicon substrate 10, which is made of acrystalline semiconductor such as monocrystalline silicon andpolycrystalline silicon. Further thereon, a transparent conductive layer(TCO) 14 is formed of indium oxide doped with tin for example, and acomb-shaped collector electrode 4 is formed of silver (Ag). On the othermain surface of the crystalline silicon substrate 10, an i-typeamorphous silicon layer and an n-type amorphous silicon layer 11 areformed in this order, and further thereon, a transparent conductivelayer 12 and a comb-shaped Ag collector electrode 5 are formed.

The solar cell element as described above is manufactured in thefollowing steps: First, by using plasma CVD method, an i-type amorphoussilicon layer and a p-type amorphous silicon layer 13 are formedsequentially on a first main surface of the crystalline siliconsubstrate 10, while an i-type amorphous silicon layer and an n-typeamorphous silicon layer 11 are formed sequentially on a second mainsurface. Next, a transparent conductive layer 14 and a transparentconductive layer 12 are formed on the amorphous silicon layer 13 and theamorphous silicon layer 11 by spattering method. Then, a comb-shapedcollector electrode 4 and collector electrode 5 are formed on thetransparent conductive layer 11 and the transparent conductive layer 14by screen printing method.

In the HIT solar cells as described above, all layers other than thecrystalline silicon substrate 10 can be manufactured by using suchmethods as plasma CVD method, spattering method, screen printing method,etc., under temperatures not higher than 200 degrees Celsius. Thisprevents distortion in the substrate while making it possible to lowermanufacturing cost. Since the HIT solar cells are manufactured inlow-temperature environment for reduced thermal damage to the amorphoussilicon layers 11, 13, the collector electrodes 4, 5 are also formed byusing resin Ag paste for low-temperature environment and curing process.For further improvement in characteristics, efforts are being made forcollector electrodes having a narrower width and rear resistance, forexample.

Then, in the HIT solar cells, a method for forming electrodes on atransparent electrode in the solar cell by plating technique isdisclosed. (See Patent Literature 1)

CITATION LIST Patent Literature

Patent Literature 1: JP-A 2000-58885 Gazette (FIG. 2)

SUMMARY OF INVENTION Technical Problem

If plating method is used to form collector electrodes, it is necessaryto ensure that plating will not be made in other regions than theregions where the collector electrodes are to be formed. This can beachieved by first forming a resist patterning film on the regions otherthan for the collector electrodes, then forming the collectorelectrodes, and then removing the resist film. This method complicatesthe manufacturing process, however.

As a solution, Patent Literature 1 proposes a method of first forming atransparent insulation layer which has an opening, on a transparentconductive layer by screen printing method, and then forming collectorelectrodes by plating in the opening where the transparent conductivelayer is exposed.

Since collector electrodes formed on the light receiving surface areobstacles in view of sunlight incident, they should desirably be low intheir resistance and narrow in their width. According to PatentLiterature 1, the transparent insulation layer with an opening is formedby screen printing, so the openings can only be narrowed to a certainlimit.

A better solution may be first coating the entire surface of thetransparent conductive layer with a transparent insulation layer, thenremoving part of the transparent insulation layer by etching or laserirradiation, to form a groove thereby exposing part of the transparentconductive layer where the collector electrodes are to be formed.

However, in the HIT solar cells, the transparent conductive layer andthe amorphous semiconductor layer have much thinner thickness, comparedwith the transparent insulation layer, so the grooves may reach thecrystalline substrate. The grooves reaching the crystalline substratedamage the junction between the crystalline substrate and the amorphoussemiconductor, resulting in decrease in photoelectric conversioncharacteristics. In order to avoid this, strict conditions must befollowed in groove formation for example, which leads to a disadvantagethat the formation step is burdensome.

An object of the present invention is to grant a margin in the controlof the depth of a groove when removing the transparent insulation layerafter the transparent insulation layer is formed on the entire surfaceof the transparent conductive layer, thereby provide a solar cell whichhas superior productivity in mass manufacturing, provide a solar cellmodule using the solar cell, and also provide a method of manufacturingthe solar cell and the solar cell module.

Solution to Problem

A solar cell provided by the present invention includes: a crystallinesemiconductor substrate of a first conductivity type; a first amorphoussemiconductor layer of the first conductivity type formed on a firstsurface of the crystalline semiconductor substrate; a first collectorelectrode formed on the first amorphous semiconductor layer; a secondamorphous semiconductor layer of a second conductivity type formed on asecond surface of the crystalline semiconductor substrate; and a secondcollector electrode formed on the second amorphous semiconductor layer.With the above, the first collector electrode is formed by plating. Thesecond collector electrode is formed by a method not impairing ajunction between the crystalline semiconductor substrate and the secondamorphous semiconductor layer, and the first collector electrode coversa smaller area than the second collector electrode.

Also, the invention provides an arrangement that the first amorphoussemiconductor layer is formed thereon with a transparent conductivelayer and a transparent insulation layer in this order, and the firstcollector electrode is formed to include a groove made in thetransparent insulation layer.

The solar cell may further include a transparent conductive layer on thesecond amorphous semiconductor layer. In this arrangement, a region inthe transparent conductive layer formed with the second collectorelectrode has the same surface profile as of the other regions in thetransparent conductive layer.

The second collector electrode may be formed by printing method or vapordeposition method, or the second collector electrode may be formed byplating method on the entire surface of the second amorphoussemiconductor layer.

Also, the first collector electrode may be placed on a light receivingside.

The present invention also provides a solar cell which includes: acrystalline semiconductor substrate of a first conductivity type; afirst amorphous semiconductor layer of the first conductivity typeformed on a first surface of the crystalline semiconductor substrate; afirst collector electrode formed on the first amorphous semiconductorlayer; a second amorphous semiconductor layer of a second conductivitytype formed on a second surface of the crystalline semiconductorsubstrate; and a second collector electrode formed on the secondamorphous semiconductor layer. With the above, the first amorphoussemiconductor layer is formed thereon with a transparent conductivelayer and a transparent insulation layer in this order. The firstcollector electrode is formed to include a groove made in thetransparent insulation layer. The second amorphous semiconductor layeris formed with a transparent conductive layer thereon. The secondcollector electrode is formed on a surface of the second transparentconductive layer, and a region in the transparent conductive layerformed with the second collector electrode having the same surfaceprofile as of the other regions in the transparent conductive layer.

The present invention also provides a solar cell module which includes aplurality of solar cells sealed between a front surface member and arear surface member. According to this solar cell module, the solar cellincludes: a crystalline semiconductor substrate of a first conductivitytype; a first amorphous semiconductor layer of the first conductivitytype formed on a first surface of the crystalline semiconductorsubstrate; a first collector electrode formed on the first amorphoussemiconductor layer; a second amorphous semiconductor layer of secondconductivity type formed on a second surface of the crystallinesemiconductor substrate; and a second collector electrode formed on thesecond amorphous semiconductor layer. With the above, the firstamorphous semiconductor layer is formed thereon with a transparentconductive layer and a transparent insulation layer in this order. Thefirst collector electrode is formed to include a groove made in thetransparent insulation layer. The second amorphous semiconductor layeris formed with a transparent conductive layer thereon. The secondcollector electrode is formed on a surface of the second transparentconductive layer. A region in the transparent conductive layer formedwith the second collector electrode has the same surface profile as ofthe other regions in the transparent conductive layer. The firstcollector electrode has a surface which faces the front surface member,and the second collector electrode having a surface which faces the rearsurface member.

Also, the solar cell module may further include a terminal box disposedon a surface of the rear surface member.

The present invention also provides a method for manufacturing a solarcell. The method includes: a step of forming an amorphous semiconductorlayer of one conductivity type on a front-surface side of a crystallinesemiconductor substrate of said conductivity type and forming anamorphous semiconductor layer of another conductivity type on arear-surface side thereof; a step of forming a transparent conductivelayer on each of the amorphous semiconductor layers; a step of forming atransparent insulation layer on the front-surface side transparentconductive layer; a step of forming an open groove which reaches thetransparent conductive layer by selectively removing the transparentinsulation layer; a step of forming a front-surface side collectorelectrode in the open groove by plating; and a step of forming arear-surface-side collector electrode on the rear-surface-sidetransparent conductive layer by printing method or vapor depositionmethod.

The opening may be formed by laser.

Advantageous Effects of Invention

According to the present invention, the first amorphous semiconductorwhich is formed on the first surface of the crystalline semiconductorsubstrate has the same conductivity type as the crystallinesemiconductor substrate, and a collector electrode is formed on thisfirst amorphous semiconductor by plating. Therefore, the inventiongrants a margin in the control of manufacturing steps such as theformation conditions and thus provides a solar cell which has superiorproductivity in mass manufacturing.

The invention also provides an arrangement that the transparentconductive layer and the transparent insulation layer are formed in thisorder on the first amorphous semiconductor layer, and the firstcollector electrode is formed to include a groove which is made in thetransparent insulation layer. In this case, there is no major problemeven if the groove has reached the substrate since the substrate and thefront-surface-side amorphous semiconductor layer have the sameconductivity type. Therefore, the invention grants a margin in thecontrol of manufacturing steps such as the formation conditions and thusprovides a solar cell which has superior productivity in massmanufacturing and a method for manufacturing it.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view which shows a structure of a solar cellaccording to an embodiment of the present invention.

FIG. 2 is a sectional view which shows a production step in amanufacturing method of the solar cell according to the embodiment ofthe present invention.

FIG. 3 is a sectional view which shows a production step in amanufacturing method of the solar cell according to the embodiment ofthe present invention.

FIG. 4 is a sectional view which shows a production step in amanufacturing method of the solar cell according to the embodiment ofthe present invention.

FIG. 5 is a sectional view which shows a production step in amanufacturing method of the solar cell according to the embodiment ofthe present invention.

FIG. 6 is a sectional view which shows a production step in amanufacturing method of the solar cell according to the embodiment ofthe present invention.

FIG. 7 is a sectional view which shows a production step in amanufacturing method of the solar cell according to the embodiment ofthe present invention.

FIG. 8 is a sectional view which shows a production step in amanufacturing method of the solar cell according to another embodimentof the present invention.

FIG. 9 is a sectional view which shows a production step in amanufacturing method of the solar cell according to said anotherembodiment of the present invention.

FIG. 10 is a sectional view which shows a production step in amanufacturing method of the solar cell according to said anotherembodiment of the present invention.

FIG. 11 is a sectional view which shows a production step in amanufacturing method of the solar cell according to said anotherembodiment of the present invention.

FIG. 12 is a plan view which shows a solar cell module according to anembodiment of the present invention.

FIG. 13 is a simplified sectional view of the solar cell moduleaccording to the embodiment of the present invention.

FIG. 14 is a sectional view which shows essential part of the solar cellmodule according to an embodiment of the present invention.

FIG. 15 is a sectional view which shows a structure of an HIT solarcell.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will be described in detail withreference to the drawings. It should also be noted that all the drawingsare conceptual sketches and may not reflect actual dimensionalproportions, etc. Therefore, information about specific dimensions, etc.should be understood and determined from the description to be givenhereafter. Keep in mind that proportional and other relationships mayalso differ from one drawing to another.

FIG. 1 is a sectional view which shows a structure of a solar cellaccording to an embodiment of the present invention. In this Figure,components which have essentially equivalent to those in FIG. 15 areindicated by the same reference symbols.

The solar cell in this embodiment differs from the conventional oneshown in FIG. 15 in that the side provided with an n-type amorphoussilicon layer 11 which has the same conductivity type as a crystallinesemiconductor substrate 10 is used as the front side, so that sun lightincident is mainly from the n-type amorphous silicon layer 11 side. Inother words, the front-rear relationship is the opposite of the ordinarysolar cells.

As shown in FIG. 1, a n-type monocrystalline silicon substrate 10 as thecrystalline semiconductor substrate has its front surface (lightreceiving surface) side formed with the n-type amorphous silicon layer11 via an i-type amorphous silicon layer. The i-type amorphous siliconlayer and the n-type amorphous silicon layer 11 are very thin films,with a combined thickness of the two layers being approximately 10 nm.On the front-surface side of the n-type amorphous silicon layer 11,there is formed a transparent conductive layer (TCO) 12 of a transparentconductive oxide such as ITO, having a film thickness of approximately100 nm. Further, on the front-surface side of the transparent conductivelayer 12, a transparent insulation layer 15 is formed of silicon oxide(SiO_(x)), etc.

On the other hand, the n-type monocrystalline silicon substrate 10 hasits rear-surface side formed with a p-type amorphous silicon layer 13via an i-type amorphous silicon layer. The p-type amorphous siliconlayer 13 has its rear-surface side formed with a transparent conductivelayer 14.

In this embodiment, plating method is employed to form a comb-shapedcollector electrode 30 on the front-surface side whereas screenprinting, vapor deposition or other method is employed to form acomb-shaped collector electrode 4 on the rear-surface-side.

In order to form the front-surface side collector electrode by plating,at least the front surface transparent insulation layer 15 on thesurface is removed in a pattern of the electrode by, for example, laser,mechanical grinding by scribing, wet etching using masks, etc. to forman open groove 2. The open groove 2 is made to a depth to reliably gobeyond the transparent insulation layer 15. During the groove makingoperation, the open groove 2 may reach the substrate 10 due to somereasons such as tolerances in formation conditions for the open groove2. This causes no major problem because the substrate 10 and thefront-surface side amorphous silicon layer 11 are of the sameconductivity type, i.e., n-type. In other words, the arrangement grantsa margin in the control of manufacturing steps such as the formationconditions of the opening groove.

Metal seeds are formed in this open groove 2, and thereafter thecollector electrode 30 is formed by plating, to have a width not greaterthan 50 μm and a height of approximately 10 μm. The collector electrode30 made by plating has a rear resistance than collector electrodes madefrom conductive resin paste, and therefore the above-mentioned width andheight provide a collector electrode which has a sufficiently lowresistance.

Since the collector electrode 30 is formed by plating on the amorphoussilicon layer 11 which has the same conductivity type as the substrate10 according to the present invention, it is possible to make the widthof the collector electrode 30 narrower than in the conventional oneswhich are formed by screen printing method or vapor deposition methodusing masks. Therefore, it is possible to reduce the area formed withthe collector electrode 30 than in the conventional solar cells. Forthese reasons, the collector electrode 30 made by plating is on thelight receiving side in the present invention. Such an arrangementreduces sun light incident loss due to the area shaded by the collectorelectrode 30, and increases the amount of light received by thesubstrate 10 accordingly. As a result, the invention improvesphotoelectric conversion characteristics.

The collector electrode 4 is formed on the p-type amorphous siliconlayer 13 which makes a p-n junction with the substrate 10. For thisreason, the collector electrode 4 is not formed by plating according tothe present invention, but is formed by a method which does not impairthe p-type amorphous silicon layer 13, such as screen printing method orvapor deposition method using masks.

Also, as mentioned earlier, the light receiving side is the side whichis formed with the collector electrode 30 in the present invention. Inother words, the collector electrode 4 is placed on the rear-surfaceside, which means sun light incident loss due to the area shaded by thecollector electrode 4 does not pose a serious concern. For this reason,the collector electrode 4 is formed to cover a larger area than thecollector electrode 30 to reduce resistance loss. Specifically, thecollector electrode 4 is made by screen printing with Ag paste, to aheight of 30 μm through 60 μm and a width of 60 μm through 200 μm and ina greater number of lines than the collector electrode 30 so that theelectrode is formed on a larger area to achieve a predeterminedresistance value. In the present embodiment the surface of thetransparent conductive layer 14 does not receive surface treatment suchas groove forming operation. Therefore, the surface of the region in thetransparent conductive layer 14 formed with the collector electrode 4remains the same as the surface of the other regions in the transparentconductive layer 14.

Also, since the transparent insulation layer 15 is transparent, thelayer has a low light-absorption loss, and therefore need not be removedafter the collector electrode has been formed by the plating operation,unlike the conventional resist. This can simplify the productionprocess.

Further, the collector electrode 30 is in contact with the surface ofthe transparent conductive layer 12 and the side surface of thetransparent insulation layer 15. In other words, the area of contact isincreased as compared to conventional ones, resulting in improvedadhesion.

The transparent insulation layer 15 can be formed with SiO₂. Otherusable material therefor includes SiN, insulating oxides such as TiO₂and Al₂O₃, and resin materials such as acrylic.

Further, when using the solar cell for power generation, normally, thesolar cells are sealed between a light receiving-side reinforced glassand a rear surface film, using a transparent sealing material such asEVA (ethylene vinyl acetate copolymer). In consideration of this, thetransparent insulation layer 15 may be designed to have a refractionindex of approximately 1.5 which is substantially the same as of thereinforced glass and of EVA mentioned above. This reduces the loss oflight caused by the transparent insulation layer 15 to a negligiblelevel. Hence, it is preferable that the transparent insulation layer 15is provided by a material which has substantially the same refractionindex as of glass, such as SiO₂.

The solar cell which has the above-described configuration according tothe present invention can be manufactured as follows:

First, as shown in FIG. 2, an i-type amorphous silicon layer and ann-type amorphous silicon layer 11 are formed sequentially on a frontsurface (a first surface) side of an n-type monocrystalline siliconsubstrate 10 by using a plasma CVD method. Likewise, an i-type amorphoussilicon layer and a p-type amorphous silicon layer 13 are formedsequentially on a rear surface (the second surface) side of thesubstrate. Next, a transparent conductive layer 12 and a transparentconductive layer 14 are formed on the amorphous silicon layer and theamorphous silicon layer 13 respectively by spattering method.

Subsequently, as shown in FIG. 3, transparent insulation layers 15, 16are formed of silicon oxide for example, on the surfaces of thetransparent conductive layer 12 and the transparent conductive layer 14respectively. The transparent insulation layers 15, 16 are formed byplasma CVD method.

Then, as shown in FIG. 4, an open groove 2 is formed by removing atleast the transparent insulation layer 15 on the surface completely inthe electrode pattern. In the present embodiment laser irradiation isused to form the open groove 2 and remove the transparent insulationlayer 15. The laser irradiation should be performed under a set ofconditions which enables removal of a very thin surface layer, so as toremove at least the insulation film 15 on the surface. For example, whenfemtosecond laser is utilized, the wavelength should be 800 nm, with thecyclic frequency of 1 kHz (a few tenth kHz through 50 kHz). The laserenergy is 1 mJ (0.3 through 20 mJ) pulse energy, with the pulse width of120 fs (50 through 250 fs).

Also, high-harmonic YVO4 laser may be used at a 355 nm wavelength forexample, under the conditions of 80 kHz (50 through 200 kHz), and 12 nS(5 through 200 nS) pulse width, and 2.5 W (1 through 10W) output at theprocessing point.

It should be noted here that the open groove 2 may be formed by othermethods than lasering. Examples include mechanical grinding such asscribing, and wet etching using masks.

In this step of making the open groove 2, only essential requirement isto reliably remove the transparent insulation layer 15. So, a certainlevel of over-etching is tolerable in forming the open groove 2 andthere is no problem even if the deepest point of the groove 2 hasreached the n-type crystalline silicon substrate 10 since the amorphoussilicon layer 11 and the substrate 10 have the same conductivity type.

Subsequently, as shown in FIG. 5, metal seeds 3 of Ag are formed in theopen groove 2. The metal seeds 3 are formed by ink-jet method orphotoelectrochemical plating method.

Thereafter, as shown in FIG. 6, the front-surface side collectorelectrode 30 is formed by electroplating using the metal seeds 3. Theelectroplating is performed on the Ag metal seeds 3 which are formed inthe open groove 2. The electroplating is performed first by activatingthe surface with sulfuric acid of 10% concentration, and then soaking awork into a plating solution in which additives are added to coppersulfate, as a negative electrode, to form a copper electrode.Thereafter, the work is soaked in a plating solution containing organicacid tin, thereby forming the copper electrode with a tin electrode tocomplete the formation of the collector electrode 30, and of the solarcell according to the present embodiment. The obtained collectorelectrode 30 by plating is a comb-shaped electrode which has a width (a)not greater than 50 μm, and a height (b) of approximately 10 μm. Then,the insulation film 16 on the rear-surface-side is removed.

Then, as shown in FIG. 7, a collector electrode 4 is formed on therear-surface-side transparent conductive layer 14 by screen printingwith Ag paste so as not to impair the p-n junction. In this collectorelectrode 4, the width and the number of lines of the electrode areincreased in order to reduce resistance. Such an adjustment asincreasing the width or the number of lines does not prevent sun lightincidence since the p-type amorphous silicon layer 13 is on therear-surface side.

As has been described thus far, the present invention provides a solarcell which has superior photoelectric conversion characteristics andmass production efficiency. Further, since removal of the collectorelectrode can be reduced, the invention provides a highly reliable solarcell.

In the embodiment described above, the rear-surface-side collectorelectrode 4 is formed by screen printing method or vapor depositionmethod, but the present invention is not limited to these. As far as asurface of the rear-surface-side transparent conductive layer 19 doesnot undergo a surface treatment such as groove making operation, therear-surface-side collector electrode may be formed by plating methodfor example.

Herein, another embodiment of the present invention, which has arear-surface-side collector electrode formed by plating method will bedescribed with reference to FIG. 8 through FIG. 11. FIG. 8 through FIG.11 are sectional views each showing a production step in a manufacturingmethod of the solar cell according to the above-mentioned anotherembodiment of the present invention.

Like the previous embodiment described earlier, an i-type amorphoussilicon layer and an n-type amorphous silicon layer 11 are formedsequentially on the front surface (first surface) side of an n-typemonocrystalline silicon substrate 10 using a plasma CVD method whereasan i-type amorphous silicon layer and a p-type amorphous silicon layer13 are formed sequentially on the rear surface (second surface) side ofthe substrate. Next, a transparent conductive layer 12 and a transparentconductive layer 14 are formed on the amorphous silicon layer 11 and theamorphous silicon layer 13 by spattering method.

Subsequently, as shown in FIG. 8, a transparent insulation layer 15 isformed of silicon oxide for example, on the surfaces of the transparentconductive layer 12. The transparent insulation layer 15 is formed byplasma CVD method. In this formation step, a transparent insulationlayer is not formed on the surface of the rear-surface-side transparentelectrode 14.

Then, as shown in FIG. 9, an open groove 2 is formed by removing atleast the transparent insulation layer 15 on the surface completely inthe electrode pattern. The open groove 2 is formed in the same method asin the previous embodiment. No treatment such as groove making isperformed to the surface of the rear-surface-side transparent conductivelayer 14.

In this step of making the open groove 2, only essential requirement isto reliably remove the transparent insulation layer 15. So, a certainlevel of over-etching may be performed in forming the open groove 2 andthere is no problem even if the deepest point of the groove 2 hasreached the n-type crystalline silicon substrate 10 since the amorphoussilicon layer 11 and the substrate 10 has the same conductivity type.

Subsequently, as shown in FIG. 10, metal seeds 3 of Ag are formed in theopen groove 2. Also, a metal seed layer 3 a is formed on the entiresurface of the rear-surface-side transparent conductive layer 14. Themetal seeds 3, 3 a are formed by ink-jet method or photoelectrochemicalplating method. Note, however, that it is not absolutely necessary toform the rear-surface-side metal seed layer 3 a.

Thereafter, as shown in FIG. 11, a collector electrode 30 is formed onthe front-surface side, and a collector electrode 40 is formed on theentire surface of the rear-surface-side transparent conductive layer 14,by electroplating using the metal seeds 3 and the metal seed layer 3 a.The electroplating is performed in the same way as in the previousembodiment.

Following the steps as described, there is obtained a solar cell whichhas a front-surface side formed with a collector electrode 30 by platingmethod, and an entire surface of the rear-surface-side transparentconductive layer 14 formed with a collector electrode 40 by platingmethod.

As described already, formation of the collector electrode 40 by platingmethod on the rear-surface-side transparent conductive layer 14 does notimpair the p-n junction since no treatment has been made to the surfaceof the transparent conductive layer 14. Therefore, the embodimentprovides the same advantages as offered by the previous embodiment.

In addition, this embodiment makes the manufacturing process evensimpler since the embodiment does not require the steps of forming andremoving the transparent insulation layer 16 which is necessary in theprevious embodiment.

Also, by using plating method, it becomes possible to lower theresistance of the collector electrode 40. The collector electrode 40which is formed all over the surface is on the rear surface, so it doesnot prevent sun light incident.

Referring to FIG. 12 through FIG. 14, a solar cell module using thesolar cell 1 according to the present invention will be described. FIG.12 is a plan view which shows a solar cell module according to anembodiment of the present invention, FIG. 13 is a simplified sectionalview of the solar cell module according to the embodiment of the presentinvention, and FIG. 14 is a sectional view which shows essential part ofthe solar cell module according to an embodiment of the presentinvention.

In the solar cell 1 which is formed as described earlier, a collectorelectrode 30 which is formed by plating is disposed on a light receivingside whereas a collector electrode 4 which is formed by printing methodor vapor deposition method is disposed on a rear-surface-side. Aplurality of this solar cell 1 are each electrically connected with theadjacent solar cells 1 with wiring members 120 which are made of flatcopper foils, etc. Specifically, each wiring member 120 has itsfirst-end side connected to the collector electrode 30 which faces afront surface member 61 side of a solar cell 1 while its second-end sideis connected to the collector electrode 4 which faces a rear surfacemember 62 side of an adjacent solar cell 1.

Thus, a plurality of the solar cells 1 are electrically connected witheach other by the wiring members 120 which are made of a conductivematerial such as copper foil, and then are sealed between the frontsurface member 61 which is transparent and is made of glass ortransparent plastic and the rear surface member 62 which is made ofweather resistant film, glass or plastic, with a transparent sealingmember 63 which has good weather resistance and moisture resistance suchas EVA.

These solar cells 1 are connected in series by the wiring members 120,so that a predetermined output of 200 W, for example, can be outputtedfrom the solar cell module 100 via transition wires 121 and powerlead-out wires 122.

As needed, an outer periphery of the solar cell module 100 describedabove is provided with an outer frame 50 which is made of aluminum forexample, by being fitted into a U-shaped in cross-section fitting part52 with a sealing member 60. The outer frame 50 is formed of aluminum,stainless steel, roll-formed steel, etc. A terminal box 70 is providedon a surface of the rear surface member 62 for example.

The embodiments described above utilize a monocrystalline siliconsubstrate as a crystalline semiconductor substrate. However,polycrystalline silicon substrates may also be used. Also, thecombination of the conductivity types in the semiconductor materials maybe different from the one described for the embodiments.

All of the embodiments disclosed herein are to show examples, and shouldnot be considered as of a limiting nature in any way. The scope of thepresent invention is identified by the claims and is not by thedescriptions of the embodiments given hereabove, and it is intended thatthe scope includes all changes falling within equivalents in the meaningand extent of the Claims.

REFERENCE SIGNS LIST

-   10 n-type monocrystalline silicon substrate-   11 n-type amorphous silicon layer-   12 transparent conductive layer-   13 p-type amorphous silicon layer-   14 transparent conductive layer-   15 transparent insulation layer-   2 open groove-   3 metal seeds-   30 collector electrode (plating)-   4 collector electrode-   61 front surface member-   62 rear surface member-   50 frame-   70 terminal box

1. A solar cell comprising: a crystalline semiconductor substrate of afirst conductivity type; a first amorphous semiconductor layer of thefirst conductivity type formed on a first surface of the crystallinesemiconductor substrate; a first collector electrode formed on the firstamorphous semiconductor layer; a second amorphous semiconductor layer ofa second conductivity type formed on a second surface of the crystallinesemiconductor substrate; and a second collector electrode formed on thesecond amorphous semiconductor layer; wherein the first collectorelectrode is formed by plating, the second collector electrode beingformed by a method not impairing a junction between the crystallinesemiconductor substrate and the second amorphous semiconductor layer,the first collector electrode covering a smaller area than the secondcollector electrode.
 2. The solar cell according to claim 1, wherein atransparent conductive layer and a transparent insulation layer areformed in this order on the first amorphous semiconductor layer, thefirst collector electrode being formed with including a groove made inthe transparent insulation layer.
 3. The solar cell according to claim1, further comprising a transparent conductive layer on the secondamorphous semiconductor layer, wherein a region in the transparentconductive layer formed with the second collector electrode has the samesurface profile as of the other regions in the transparent conductivelayer.
 4. The solar cell according to claim 1, wherein the secondcollector electrode is formed by printing method or vapor depositionmethod.
 5. The solar cell according to claim 1, wherein the secondcollector electrode is formed by plating method on an entire surface ofthe second amorphous semiconductor layer.
 6. The solar cell according toclaim 1, wherein the first collector electrode is placed on a lightreceiving side.
 7. A solar cell comprising: a crystalline semiconductorsubstrate of a first conductivity type; a first amorphous semiconductorlayer of the first conductivity type formed on a first surface of thecrystalline semiconductor substrate; a first collector electrode formedon the first amorphous semiconductor layer; a second amorphoussemiconductor layer of a second conductivity type formed on a secondsurface of the crystalline semiconductor substrate; and a secondcollector electrode formed on the second amorphous semiconductor layer;wherein a transparent conductive layer and a transparent insulationlayer are formed in this order on the first amorphous semiconductorlayer, the first collector electrode being formed with including agroove made in the transparent insulation layer, the second amorphoussemiconductor layer being formed with a transparent conductive layerthereon, the second collector electrode being formed on a surface of thesecond transparent conductive layer, a region in the transparentconductive layer formed with the second collector electrode having thesame surface profile as of the other regions in the transparentconductive layer.
 8. A solar cell module comprising a plurality of solarcells sealed between a front surface member and a rear surface member,wherein the solar cell comprising: a crystalline semiconductor substrateof a first conductivity type; a first amorphous semiconductor layer ofthe first conductivity type formed on a first surface of the crystallinesemiconductor substrate; a first collector electrode formed on the firstamorphous semiconductor layer; a second amorphous semiconductor layer ofa second conductivity type formed on a second surface of the crystallinesemiconductor substrate; and a second collector electrode formed on thesecond amorphous semiconductor layer; wherein a transparent conductivelayer and a transparent insulation layer are formed in this order on thefirst amorphous semiconductor layer, the first collector electrode beingformed with including a groove made in the transparent insulation layer,the second amorphous semiconductor layer being formed with a transparentconductive layer thereon, the second collector electrode being formed ona surface of the second transparent conductive layer, a region in thetransparent conductive layer formed with the second collector electrodehaving the same surface profile as of the other regions in thetransparent conductive layer, the first collector electrode having asurface facing the front surface member, the second collector electrodehaving a surface facing the rear surface member.
 9. The solar cellmodule according to claim 8, further comprising a terminal box disposedon a surface of the rear surface member.
 10. A method for manufacturinga solar cell, comprising: forming an amorphous semiconductor layer ofone conductivity type on a front-surface side of a crystallinesemiconductor substrate of said conductivity type and forming anamorphous semiconductor layer of another conductivity type on arear-surface side thereof; forming a transparent conductive layer oneach of the amorphous semiconductor layers; forming a transparentinsulation layer on the front-surface side transparent conductive layer;forming an open groove which reaches the transparent conductive layer byselectively removing the transparent insulation layer; forming afront-surface side collector electrode in the open groove by plating;forming a rear-surface-side collector electrode on the rear-surface-sidetransparent conductive layer by printing method or vapor depositionmethod.
 11. The method for manufacturing the solar cell according toclaim 10, wherein the opening is formed by laser.